1. Field of the Invention
The present invention relates to a projection lens and a projector having the projection lens.
2. Description of Related Art
Conventionally, a projector having a plurality of liquid crystal panels for modulating a plurality of color lights for each color in accordance with image information, a cross dichroic prism for combining the color lights modulated by the respective liquid crystal panels, and a projection lens for enlarging and projecting the light beam combined by the prism has been used.
A projection lens used for such projector is a composite lens constructed by a plurality of lenses including a convergent lens and a divergent lens in order to restrain deterioration of resolution and distortion aberration and chromatic aberration of projected image. However, the optical axis (core) position of the respective lenses of the projection lens has to be adjusted with high accuracy in order to function the lens and maintain the quality of the projected image. Such projection lens capable of adjusting optical position is disclosed in, for instance, Japanese Patent Laid-Open Publication No. 2000-66076 (Page 3, FIG. 3).
FIG. 22 is a cross section showing an example of the conventional projection lens. In FIG. 22, a projection lens 900 has a lens 910, a lens barrel 920 with the lens 910 being fixed therein (referred to as exterior case 920), and a stopper 930 for securing the lens 910 on the exterior case 920.
The exterior case 920 has a first exterior case 921 and a second exterior case 922 slidably provided on the first exterior case 921, where the optical axes of the first exterior case 921 and the second exterior case 922 are aligned.
The projection lens 900 has a first group lens 911, a second group lens 912 and a third group lens 913 fixed on the first exterior case 921, and a fourth group lens 914 fixed on the second exterior case 922.
The stopper 930 collectively refers to the components for fixing the respective group lenses on the exterior case.
A stopper 907 of a lens adapter 908 of the second group lens 912 has an inner wall abutted to a lens-tilting eccentric pin 931 and an outer wall pressed by an O-ring 960, which is supported by an O-ring stopper 970 screwed to the first exterior case 921. In other words, the second group lens 912 is fixed through the O-ring 960.
FIG. 23 is a schematic illustration of the lens-tilting eccentric pin of the conventional projection lens, where FIG. 23A is a cross section taken along a surface orthogonal with an axis core of the first exterior case 921 and FIG. 23B is a side elevation with a partial cross section.
A lens-tilting through-hole 923 is provided on the side of the first exterior case 921 in a plane perpendicular to the axis of the exterior case 920 (referred to as X-Y plane hereinafter) at a constant interval (120 degrees) along circumference thereof. In the figure, the component is attached with additional signs of s, t and u for respective directions. A lens-tilting eccentric sleeve 932 is respectively provided on the lens-tilting through-hole 923 in a rotatable manner.
When the lens-tilting eccentric sleeve 932 is rotated, the lens-tilting eccentric pin 931 guides the lens adapter 908 in a direction perpendicular to the X-Y plane, so that the second group lens 912 engaged by the lens adapter 908 is inclined. In other words, the second group lens 912 is “tilted”.
However, in the conventional arrangement, though the tilt of the group lens can be adjusted by fixing the group lens by the lens-tilting eccentric pin, it is impossible to move the group lens in parallel without changing the inclination of the optical group (e.g. movement parallel to the axis of the exterior case: referred to as shift adjustment hereinafter). Accordingly, even when the shift adjustment of the optical axis is necessary relative to the exterior case in which the group lens is provided or the other adjacent group lens, such shift adjustment cannot be conducted.